Turbomachines encompass generally continuously working fluid energy machines such as compressors, steam turbines and gas turbines. A gas turbine converts energy from a hot combustion gas into kinetic energy which drives, on one hand, a compressor connected upstream and, on the other hand, typically an electricity generator. A gas turbine can however also be used to power aircraft.
Gas turbines comprise, on one hand, stationary guide vanes which guide the flow of air and gas and, on the other hand, gas turbine rotor blades which rotate about the axis of the turbomachine and form rotor blade rings which are arranged one behind another in the axial direction. The rotor blades typically extend from the axis of the turbomachine to an internal wall arranged coaxially therewith, which thus defines the flow channel for the combustion gas. In this context, the clearance between the body of the rotor blade and the internal wall must be kept as small as possible in order to minimize the loss of efficiency due to combustion gas flowing past the rotor blades along the internal wall.
However, the clearance between the internal wall and rotor blade tips located opposite this can vary due to differential thermal expansion of the internal wall and the rotor blade, centrifugal forces and radial accelerations, and also assembly play of the components in question. In such cases, in order to avoid damage to the rotor blade body and/or to the internal wall, a certain minimum clearance must be planned when building the gas turbine. Damage of this nature could in particular result in reduced life of the rotor blades or of the internal wall.
Furthermore, various optical systems for measuring the radial gap during operation of turbomachines are known, for example from U.S. Pat. No. 4,049,349 A1 and GB 2 069 689 A1. What is more, it is known from U.S. Pat. No. 6,898,547 A1 to use sensors to determine the radii of two adjacent rotor components in order to achieve reliable assembly of the rotor components.